In recent years, an optical transport network (OTN) is being standardized in International Telecommunication Union-Telecommunication sector (ITU-T) and Institute of Electrical and Electronic Engineers (IEEE).
The OTN can transmit different kinds of client signals in a transparent manner in an optical network to which a wavelength division multiplexing (WDM) technique is applied.
As a method that is high in reliability on a failure and capable of effectively using network resources in the OTN, there is a shared restoration scheme (for example, see WO2004/075494).
In the shared restoration scheme, a band of a protection path placed in a route completely different from a working path is secured in advance, and a band of one protection path is shared by a plurality of working paths. When a failure occurs in the working path, a control signal such as an automatic protection switching (APS) signal is transmitted in the protection path to secure a physical connection of the protection path and perform switching from the working path to the protection path.
FIG. 37 illustrating an exemplary network configuration in the shared restoration scheme. For example, a network illustrated in FIG. 37 includes communication nodes #1 to #11, and the communication nodes #1 to #11 are connected in a mesh form, for example.
A working path A is set to a route passing through the communication nodes #1, #2, #3, and #4. Further, a working path B is set to a route passing through the communication nodes #8, #10, #11, and #9. For each of the working path A and the working path B, a physical connection setting is secured in the corresponding communication node #j (j=one of 1 to 11).
Meanwhile, a protection path A for the working path A is set to a route passing through the communication nodes #1, #5, #6, #7, and #4. Further, a protection path B for the working path B is set to a route passing through the communication nodes #8, #5, #6, #7, and #9.
The protection paths A and B are in a state in which a physical connection setting has not been secured in the corresponding communication node #j but a band has been reserved. Further, between the communication node #5 and the communication node #7, reserved bands of the protection paths A and B are shared by the working path A and the working path B.
When a failure occurs in the working path A (or the working path B), path switching is performed so that a signal (traffic) which has been transmitted through the working path A (or the working path B) is available to be transmitted through the protection path A (or the protection path B).
Here, WO2004/075494 discloses a method of switching a path quickly in the shared restoration scheme. FIG. 38 illustrates an exemplary network configuration before a failure occurs, and FIG. 39 illustrates an exemplary network configuration when a single failure occurs.
As illustrated in FIG. 38, a physical connection setting is secured before a failure occurs in each of the communication nodes #1, #5, #6, #7, and #4 positioned in the route through which the protection path A passes. Meanwhile, in each of the communication nodes #8, #5, #6, #7, and #9 positioned in the route through which the protection path B passes, a physical connection setting is not secured, and a protection path band is reserved.
Further, a failure is assumed to occur in the working path A (for example, between the communication nodes #2 and #3) as illustrated in FIG. 39. In this case, since physical connection is secured between the communication nodes #1 and #4 respectively corresponding to a source node and an end node of the protection path A, by performing an APS switching process in the end node #4, fast path switching from the working path A to the protection path A can be performed.
However, when a failure occurs in the working path B, a physical connection setting is not secured in the protection path B. Thus, it is necessary to transmit a control signal such as an APS signal from the communication node #8 to the communication node #9 through the communication nodes #5 to #7 to secure the physical connection setting of the protection path B. After the physical connection setting of the protection path B is secured, switching the working path B to the protection path B is performed.
As described above, in the shared restoration scheme, among a plurality of working paths sharing the protection path, only one working path can secure the physical connection in the protection path in advance. Thus, when a failure occurs in the working path that does not secure the physical connection in the protection path in advance, since it is necessary to transmit a control signal after detecting the failure, and thus it is unavailable to switch the working path to the protection path quickly.